The present invention relates generally to equipment for use in subterranean wells and, in a preferred embodiment thereof, more particularly provides a retrievable screen apparatus and methods of using the apparatus.
Sand control screens are utilized for various purposes in subterranean wells. The name derives from their early use in preventing the production of sand along with fluids from formations. A sand control screen is typically suspended from production tubing extending to the earth's surface and positioned in a wellbore opposite a productive formation. In this way, the sand control screen may exclude the produced sand while permitting the valuable fluids to enter the tubing for transport to the earth's surface.
Other operations in which sand control screens are utilized include fracturing and gravel packing. In fracturing and gravel packing operations, material known as "proppant" or "gravel" is usually suspended in a slurry and pumped down the tubing and into the annular space between the sand control screen and metal casing lining the wellbore. The material typically accumulates in the annular space and eventually fills it, completely covering the exterior surface of the screen. The sand control screen prevents this material from being pumped back to the earth's surface.
Since it is generally not possible to pump gravel or proppant through the screen, other flow passages are typically provided in a fracturing and/or gravel packing apparatus to permit fluid communication between the tubing and the annular space. These other flow passages must then be closed when it is desired to produce fluids from the formation, which usually requires mechanical or pressure-operated devices, or manipulation of the tubing.
In some situations, it is necessary to filter very fine particles from the produced formation fluids. High filtration screens are used in these situations. Unfortunately, such high filtration screens usually become clogged with debris relatively quickly. Therefore, it is advantageous for high filtration screens to be retrievable, so that they may be periodically retrieved and either replaced, or cleaned and reinstalled. In addition, it would be desirable for a high filtration screen to have a low filtration screen disposed between the high filtration screen and the annular space, so that the high filtration screen would not become clogged as quickly, and so that the low filtration screen will prevent production of large sand particles or other debris when the high filtration screen is retrieved for cleaning or replacement.
It is well known in the art for a screen to be retrievably attached to, and suspended from, production tubing. Such screens provide a means of retrieval and replacement of the screens adjacent a productive formation. They do not, however, permit fracturing or gravel packing operations therethrough since an open end of the tubing is exposed when the screen is not in place. They also have no provision for placement of a low filtration screen between a high filtration screen and the produced formation.
From the foregoing, it can be seen that it would be quite desirable to provide a retrievable screen which may be installed in tubing or attached to a packer, which may have a low filtration portion between a high filtration portion and a producing formation, and which may be utilized in association with other operations, such as fracturing and gravel packing operations. It is accordingly an object of the present invention to provide such a retrievable screen apparatus and methods of using the apparatus.